The liquids that line the surface of the lung are critical for the maintenance of lung health. Focusing on CFTR, ENaC, and extracellular purines/purinoceptors, the PPG proposes to elucidate the molecular mechanisms that 1) regulate pulmonary surface liquid at local levels and 2) integrate airway and alveolar pulmonary surface liquid physiologies. To accomplish these goals, the PPG requires four Projects. Project I (Dynamics and Thermal Stability in CFTR Function and Dysfunction, J. R. Riordan, Ph.D., P.l.) proposes to study the mechanisms that confer temperature stability to wild-type CFTR, and, importantly, the temperature instability at physiologic temperatures of ?F508 CFTR. Project II (CFTR-ENaC Regulatory and Structural Interactions in Human Airway Epithelia, M.J. Stutts, Ph.D., P.l.) proposes to study the molecular basis for the regulatory relationship between CFTR and ENaC in airway epithelia at the structural, functional, and the regulatory levels. Project III (Purinergic Control of CFTR-ENaC Interactions in Alveolar Epithelia, R.C. Boucher, M.D., P.l.) proposes to study purinoceptor regulation of the CFTR-ENaC interrelationship on alveolar surfaces, focusing on the dominance of purinoceptor inhibition of ENaC in controlling the direction of alveolar liquid flow. Project IV (Mechanisms and Consequences of Nucleotide Release in the Lung, E. R. Lazarowski, Ph.D., P.l.) will investigate the mechanisms, regulation, and consequences of nucleotide release in airway epithelia, investigating the relative roles of vesicular vs. conductive release paths in health and their contribution to the pathogenesis of major airways diseases. The PPG Projects are supported by three Cores: an Administrative Core; a Cell Culture Core; and a Molecular Biology Core. By focusing on three major themes, i.e., CFTR, ENaC, and purinoceptor ligand-receptor interactions, from molecular to systems biology length scales, the PPG proposes to 1) generate a detailed molecular understanding of the regulation of Ion channel number/activity for local pulmonary surface liquid homeostasis and 2) integrate these activities over the entire surface of the lung to provide the framework for understanding normal physiology, disease pathogenesis, and design of novel therapies for major human lung diseases.